Trace metals are important, both as essential constituents, and as poisons of living organisms. Many metal ions such as zinc and cadmium possess few spectroscopic properties with which to probe their structural and functional role in proteins. We propose to show that the vanadyl ion (VO super 2 plus), which has several unique chemical and spectroscopic properties, would make an ideal label of general use of investigating metal binding sites in proteins. Procedures for introducing vanadyl into proteins will be developed. The use of metal ions in inhibition of enzymes, as enzyme constituents, and in protein conformation and subunit assembly will be investigated primarily through vanadyl epr spectroscopy. Binding constants of non- spectroscopic metals such as zinc will be determined through competitive binding with vanadyl. The specific projects to be undertaken are: (1) The binding of vanadyl to amino acids and peptides, (2) a single crystal study of the vanadyl insulin molecule, (3) the inhibition of lysozyme by metal ions, (4) heavy metal poisoning with serum albumin as a model system, and (5) metals in the metalloenzymes carbonic anhydrase and carboxypeptidase. It is intended that these studies will illustrate the wide range of applicability of the proposed vanadyl labeling method, provide needed baseline data for future work, and encourage the general use of this heretofore unexploited approach to the study of metal binding to biopolymers.